The invention pertains to a system for installation of a resonating needle type liquid injector, intended in particular for a thermal engine.
From document FR 2 889 257 one is familiar with an injector whose opening is achieved by placing a needle in resonance. Such a device comprises a tubular body, an injector nose prolonging the tubular body. A needle is lodged in the nose, extending lengthwise in the form of a rod. One end of the needle comprises a head forming a valve on a seat carried by the nose. The device also comprises an actuator able to cause a displacement of the head to open the valve by placing the needle in axial resonance with axial impulses at a given nominal frequency. The nominal frequency is typically between 15 and 30 kHz, but it can be higher.
During the functioning of the device, the head of the needle comes to bear against the seat before moving away from it, leaving an opening for the fuel between them. The nose is thus subjected to axial impulses which also have a tendency to place it in resonance. One thus chooses preferably a nose shape with a constant cross section and a length that is close to a multiple of the half-wavelength for the nominal frequency. Thus, the resonance of the nose favors that of the needle, boosting the amplitude of the opening of the injector.
However, for classical metal materials such as steel, this condition translates into a substantial length of nose as compared to the classical thickness of a cylinder head wall. If the base of the nose, opposite the seat, serves as a support for the device against the cylinder head, the nose will project into the combustion chamber where the fuel is supposed to be injected. But this is not compatible with the space constraints in the combustion chamber or with the thermal constraints that the device can withstand.